Hi,

I have a wafer, which contains some deep trenches. I fabricated these 250
micron deep trenches using DRIE, with AZ9260 as the mask layer. Now I have
to do a DRIE, to etch away 150 micron more, in the trenches already
fabricated as well as in some other regions.

In order to do this 2 level DRIE, I had grown an oxide layer 2 microns thick
to act as the masking layer for the second DRIE. I had planned to use 9260
as the masking layer for the first DRIE and the oxide as the masking layer
for the second DRIE. However after growing the oxide layer, and etching away
the unwanted regions, I found that some of the masking oxide layer has also
been removed.

As I said for the first DRIE, I used 9260, and the DRIE went fine. I had
initially thought that I would use the 9260 layer which would remain after
the DRIE and do a contact exposure-development, to expose the areas where I
wanted the next DRIE to happen. This would help me do the DRIE on regions I
wanted to expose, to circumvent the problem created by the presence of the
holes in oxide layer.

However after the first DRIE I found that the 9260 layer has become complete
inert to the the developer AZ 400K, even after multiple and long expsures.

Next, I removed the 9260 on one of the test wafers, and tried doing a
contact exposure-development with various photoresists in AZ and SC series.
In all of them I found that even after long exposures, some of the
photoresist always remains within the trenches, and I cannot remove that. I
am not sure why this happens.

So I wonder if somebody could help me with these questions:

a) how do I do a fabricate a photoresist based masking layer for a wafer,
which already contains deep trenches of ~ 250 microns?

b) Is it possible to activate the photoresist top surface after a DRIE, so
that I can do a contact exposure-development on the photoresist already
present?

--
Thanks

Dibyadeep Paul